No official cause of death was available. Antonia Ferrier, a spokeswoman for Boehner (R-Ohio), said it appeared that Ms. Nowakowski died of a heart attack.

A longtime Hill aide, and Boehner's staff chief since 2006, Ms. Nowakowski was named by the Capitol Hill publication Roll Call to its 2009 list of the "Fabulous Fifty" staff members. The accolade recognized her savvy, her clout and her access to the top people in Congress.

Ms. Nowakowski, an avowed conservative, was highly regarded by leaders of both parties.

"It is with profound sadness and shock that I announce the passing of Paula Nowakowski, my longtime chief of staff, trusted aide, and friend, who died suddenly," Boehner said in a statement.

"Words cannot adequately express the sorrow and disbelief I and every member of our team are grappling with today in the wake of this stunning news," Boehner said.

Pelosi called Ms. Nowakowski a "thorough professional who loved the House and worked in a constructive and bipartisan fashion to implement policies to help the Congress function efficiently."

According to WhoRunsGov. com, a Washington Post Co. Web site, Ms. Nowakowski grew up in St. Clair Shores, Mich., and studied English at Cornell University in Ithaca, N.Y.

She told Politico of being made more conservative by the campus "rise of the loony left," citing "wacky, wacky stuff," which shaped her politics.

According to a reference book on congressional aides, she worked for the Republican National Committee in the late 1980s and early 1990s, then joined the staff of the House Republican Conference. After two years as a public affairs vice president of the American Insurance Association, she worked from 2001 to 2006 as staff director of the House Committee on Education & the Workforce. A Boehner aide said she worked for him at both the Republican Conference and the Education Committee.

Pelosi's staff chief, John Lawrence, who was Ms. Nowakowski's Democratic counterpart on the education committee, said they transcended political differences to "work in a very collegial way to strengthen the House itself." He called her "a great professional."

After the GOP lost its House majority in 2006 , Ms. Nowakowski said she experienced "the seven stages of grief," according to the Almanac of the Unelected 2008, a reference on Hill staffers.

"You don't want to be a compliant minority," she said of the party's new status, "but you have to adjust your expectations."